The present invention generally relates to a machine tool such as, for example, a drill or an end milling machine and, more particularly, to a chuck assembly for the machine tool for holding a tool, for example, a heavy-duty cutting tool.
A typical prior art chuck assembly of the type referred to above is disclosed in, for example, the Laid-open Utility Model Publications No. 58-143107 and no. 58-143108 both filed in Japan in the name of the same assignee of the present invention and first published in 1983. To sum up, the chuck assembly disclosed in any one of these publications may be considered corresponding to a chuck assembly according to the present invention from which an internally threaded reinforcement ring employed in accordance with the teachings of the present invention as shown in FIG. 1 of the accompanying drawings is eliminated.
For the purpose of the discussion of the prior art, the prior art chuck assembly will be described with the aid of FIG. 1 which illustrates a preferred embodiment of the present invention as will be described later. As shown, the prior art chuck assembly comprises a generally cylindrical body 1 having a radially outwardly protruding collar 2 and an axially outwardly tapering shank 3 formed integrally therewith and positioned on respective ends of the cylindrical body 1, and a sleeve 4 extending axially outwardly from one end of the cylindrical body 1 where the collar 2 is formed radially outwardly. The sleeve 4 is adapted to receive therein and support a tool element (not shown) such as, for example, a cutter or a drill, and for this purpose, takes a cross-sectional representation such as shown in any one of FIGS. 2(a), 2(b), 2(c), 2(d) and 2(e). In other words, the sleeve 4 takes a cross-sectional representation wherein the wall is rendered to have a relatively small thickness or is axially splined to provide circumferentially equidistantly spaced sleeve segments so that the sleeve 4 can be radially inwardly deformed or constricted to firmly chuck the tool element. The sleeve 4 has its outer peripheral surface 4a tapered in a direction axially away from the cylindrical body 1 and has a fastening ring or nut 6 rotatably mounted thereon, said fastening nut 6 having its inner peripheral surface tapered in complementary relation to the inner peripheral surface 4a of the sleeve 4.
A plurality of roll bearings 7, each comprised of a roller retainer 8 retaining non-detachably, but loosely a plurality of, for example, two needle rolls, are circumferentially disposed between the outer peripheral surface of the sleeve 4 and the inner peripheral surface of the fastening nut 6 with the longitudinal axis of each of the needle rolls extending in inclined relation to the generatrix of the tapering of any one of the inner and outer peripheral surface of the fastening nut 6 and the sleeve 4, respectively. Accordingly, as the fastening nut 6 is rotated in one direction about the sleeve 4, that is, the longitudinal sense of the chuck assembly, the fastening nut 6 can be axially moved in one direction, for example, towards the cylindrical body 1 together with the roll bearings 7 to cause the sleeve 4 to be radially inwardly deformed or constricted with a support bore 5 consequently reduced in its diameter to firmly chuck the tool element. This is possible because the outer peripheral surface 4a of the sleeve 4 and the inner peripheral surface of the fastening nut 6 are so shaped as to be complementary with each other and are so tapered that, when the fastening nut 6 is axially moved leftwards as viewed in FIG. 1 by turning it around the sleeve 4, the free end portion of the sleeve 4 remote from the cylindrical body 1 can be radially inwardly yielded to reduce the diameter of the support bore 5 for the receipt of the tool element, thereby firmly chucking the tool element then inserted in the support bore 5.
In this prior art chuck assembly of the construction described hereinabove, since the sleeve 4 is so formed as to have a considerably reduced wall thickness, it has been found that during the use of the chuck assembly in operation, the sleeve 4 tends to oscillate to produce a rattling sound, thereby hampering a precise machining operation.
In order to overcome the previously discussed problem, it can be contemplated to provide a chuck assembly wherein the sleeve having a considerably reduced wall thickness, the fastening nut mounted exteriorly on the sleeve, and a portion of the cylindrical body, for example, the collar having a wall of greater thickness can be integrally rotated together during the use of the chuck assembly in operation. Another conventional chuck assembly embodying this concept is shown in FIG. 5.
According to the prior art shown in FIG. 5, the collar 2 is integrally formed with an annular projection 9 protruding towards the fastening nut 6 and has an annular hard rubber lining 10 secured to the annular end face of the projection 9 such that, when the fastening nut 6 is fastened while axially moved leftwards, the annular end face of the fastening nut 6 adjacent the hard rubber lining 10 can be brought into contact with the annular hard rubber lining 10 with the hard rubber lining 10 consequently compressed to permit the sleeve, the fastening nut and the collar to be integrated together.
However, the prior art chuck assembly which utilized the rubber lining has a drawback in that the amount of deformation of the rubber lining incident to the internal compression resulting from the engagement of the fastening nut is so limited that the fastening nut when fastened cannot be firmly coupled with the cylindrical body. In other words, depending on the type of the tool element, the outer diameter of the shank is smaller than the internal diameter of the sleeve and, therefore, in order for the tool element to be firmly chucked, the extent to which the sleeve should be radially inwardly deformed or constricted for the purpose of firmly chucking the tool element must be sufficiently great. However, with the prior art chuck assembly utilizing the rubber lining to which the fastening nut 6 is brought into engagement under pressure when the fastening nut 6 is fastened, the rubber lining 10 cannot be sufficiently internally compressed to firmly chuck the tool element.